The present invention relates to a copolymeric and amphiphilic precursor of polyimide, a process for the preparation thereof, and thin films, and more particularly to a copolymeric amphiphilic polyimide precursor modified so as to form a film by the Langmuir-Blodgett technique.
In the 1930s, it was found by Langmuir and Blodgett that a fatty acid having 16 to 22 carbon atoms could form a monolayer (monomolecular film) on the surface of water and the monolayers could be built up on a substrate to form a multilayer film. In recent years, various studies have been made on the applications of the built-up films, namely Langmuir-Blodgett films (hereinafter referred to as "LB film"). The LB films of the straight-chain saturated fatty acids are poor in heat resistance and mechanical strength and are not suitable for practical uses. In order to solve the above problem, there are proposed, for instance, polymerizing films formed from unsaturated fatty acids such as .omega.-tricosenoic acid, .omega.-heptadecenoic acid and .alpha.-octadecylacrylic acid, or unsaturated fatty acid esters such as vinyl stearate and octadecyl acrylate. However, these films are insufficient in heat resistance and other properties.
On the other hand, it is well known that films of polyimide have excellent heat resistance. The thickness of the films prepared, for instance, by spin coating is at least 1,000 .ANG., usually 1 .mu.m or more. It is very difficult to form a heat resistant polyimide film with a thickness of less than 1,000 .ANG. and with no pin-hole.
It is an object of the present invention to provide an LB film having improved heat resistance, chemical resistance, mechanical properties such as adhesion and good insulation properties.
A further object of the present invention is to provide a material capable of providing a heat resistant ultrathin film.
A still further object of the present invention is to provide ultrathin films of copolymeric polyimides.
These and other objects of the present invention will became apparent from the description hereafter.